Sifelani Tsiko, Innovations Editor — The latest tremor with a magnitude of 4,9 experienced in Kariba and surrounding areas on December 23 has not affected the structural integrity of the Kariba Dam which was built about 61 years ago, the Zambezi River Authority (ZRA) has said.
The authority which manages the Kariba Dam on behalf of the Zimbabwean and Zambian governments, confirmed the occurrence of heightened seismic activity in Kariba and surrounding areas this month.
The epicentre of the first six earthquakes on December 7, 8 and 11, with a magnitude ranging between 4,1 and 4,7 was located between 19km and 40km south-south-east of Kariba town in the Charara Safari Area.
A magnitude 4,3 earthquake incident on December 11, the seventh was triangulated approximately 106km away from Kariba Dam in the Hurungwe District while the epicentre of the most recent earthquake incident on December 23 was approximately 10km within the Kariba reservoir, directly behind the Antelope Island in Zimbabwe.
“Within this context, the earthquakes that have been experienced in Kariba, Siavonga and surrounding areas since the construction of the Kariba Dam are relatively small and have not generated large ground accelerations or vibrations as to cause concern regarding the safety of the dam wall,” the ZRA said in a latest update.
“The inspections and analysis of data from the various monitoring instruments after the earthquakes referred to above did not reveal any unusual observations and the dam continued to exhibit normal behaviour that is consistent with prevailing loading conditions.”
Tremors of such a nature are a common occurrence in the area around the Kariba Dam.
Experts refer to these tremors as load induced tremors, or specifically reservoir induced tremors in the case of the Kariba Dam, and are a result of the earth crust’s response to the water load or weight of water given the size of the dam.
Ever since 1963 when the Kariba Dam started filling, more than 1 000 tremors of magnitude 4.0 have been experienced.
The earthquakes are not only peculiar to Kariba, but have also been reported from the filling and subsequent operation of several other large dams and reservoirs worldwide.
Most tremors around Lake Kariba have been barely perceptible to humans. These reservoirs induced seismic events pose little risk of damage to buildings or humans.
They are better described as tremors or more neutrally as seismic events rather than the more emotive — though common — term earthquake.
